1. Field of the Invention
The present invention relates to a device for inserting a deformable intraocular lens into the eye. Examples of such a deformable intraocular lens include a deformable intraocular lens that is inserted into the eye in place of the natural lens when the latter is physically extracted because of cataracts, and a vision correction lens that is inserted into the eye for the sole purpose of vision correction.
2. Description of the Related Art
In general, during cataract surgery, an intraocular lens is inserted into the eye, from which the natural lens has been removed (lens-removed eye), such that the intraocular lens is located in the original position previously occupied by the natural lens and restores vision. Various studies on the material and shape of such an intraocular lens have been carried out since Ridley performed the first implantation of an artificial lens in 1949.
In recent years, in addition to studies on intraocular lenses which are used for vision restoration after cataract surgery, intense studies on intraocular lenses for refractivity correction have been ongoing. Such an intraocular lens for refractivity correction is inserted into the eye which still has a natural lens (lens-carrying eye), for correction of nearsightedness or farsightedness.
In relation to cataract surgery, a technique for crushing the lens tissue by means of ultrasonic emulsification and suctioning the crushed tissue away has been popularized. This technique enables performance of lens removal surgery to excise an opaque lens through a small incision. Along with progress in the operational technique itself, intraocular lenses themselves have recently been improved. Such an improved intraocular lens is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 58-146346. In the intraocular lens, the optical portion is made of a deformable elastic material. The intraocular lens is inserted, in a folded state, into the eye through a small incision and restored to its original shape within the eye allowing it to exert its proper lens function.
Accompanying these technical developments, the material of the optical portion of such an intraocular lens has been changed gradually from hard polymethyl methacrylate (PMMA) to silicone or soft acrylic resin, which enables the intraocular lens to be inserted into the eye in a folded state.
Moreover, in recent years, studies have been conducted on copolymers such as hydroxyethyl methacrylate and methyl methacrylate, as well as on hydrophilic materials such as 2-hydroxyethyl methacrylate (HEMA).
Further, intraocular lenses of different shapes have been studied and put into practical use, including an intraocular lens having a circular optical portion and loop-shaped support portions formed of different materials, an intraocular lens whose loop-shaped support portions and optical portion are formed of the same material, and an intraocular lens having plate-shaped support portions.
Furthermore, the following patent publications disclose insertion devices for inserting the above-described deformable intraocular lens into the eye in a compressed or folded state.
(1) Japanese Patent Application Laid-Open (kokai) No. 5-103803 discloses a device designed such that a holding member which holds a folded lens is attached to a main body, and the lens is inserted into the eye through an insertion tube provided at the tip end of the holding member.
(2) Japanese Patent Application Laid-Open (kokai) No. 7-23991 discloses a disposable insertion device for one-time use in which a portion for holding a folded lens is integrated with a main body of the device and the entirety of the device is formed of resin.
The above-described are typical examples of conventional intraocular-lens insertion devices, which are divided into various types in accordance with their mechanisms for folding an lens; such as a type in which a lens is folded by use of a taper portion of a holding member, and a type in which a lens is folded by use of a hinged portion of a holding member.
However, a conventional intraocular-lens insertion device of the former type in which a lens is folded by use of a taper portion of a holding member involves the following problem. Since a space of the holding member for placement of an intraocular-lens is large, the posture of a push rod within the space cannot be controlled, and consequently the push rod deflects in the course of a step of advancing the push rod.
When the push rod deflects, the intraocular lens may be caught between the inner wall surface of the holding member and the push rod with resultant breakage of the intraocular lens, or a tip end portion of an insertion tube of the insertion device may be broken.
Meanwhile, the tip end portion of the push rod, which provides a function of pushing the intraocular lens out of the insertion device, has a diameter that is determined in accordance with the inner diameter of the insertion tube at its tip end. Therefore, in the intraocular-lens insertion device of the type in which a lens is folded by use of the taper portion (i.e., the insertion tube), the tip end of the push rod cannot be formed to have a large diameter, even though the insertion device has a large space at its lens placement section. Accordingly, when the intraocular lens is pushed out, a large load or pressure acts on the intraocular lens.